The present invention relates to a device for separating slag from molten metal as the molten metal is transferred from a receptacle.
In metal making processes, a layer of slag comprising metal impurities forms atop the surface of molten metal held within a metal receptacle such as a furnace, tundish or ladle. As the molten metal is drained from the receptacle, the flow of molten metal through the discharge induces a swirl above the discharge nozzle. At a critical level, the energy of the swirl creates a vortex, whereby the slag layer is sucked into the nozzle, thus contaminating the pour. Separation of the slag and molten metal enhances the quality of the discharge.
Several devices have been known to inhibit the introduction of the slag into the nozzle via the sucking effect of the nozzle. Many of the previously known devices for restricting slag flow through the discharge nozzle were in the form of a refractory body and extending rod combination. For example, the abstract of German Disclosure DE 19821981 A1 to Stilkerieg discloses a slag retainer consisting of a closure body and a finned guide bar. The fin elements consist of a refractory material, preferably a refractory concrete. The closure body also has a bar protruding perpendicularly upwards from the base of the closure body. This bar is attachable to an arm which positions the slag retainer over the tapping channel. Although suitable for its intended purpose, the fin elements are expensive to fabricate. Therefore, the use of a finned guide bar substantially increases the costs of metal making. Moreover, the extending rod enters the tap hole and stifles the flow of molten metal through the nozzle during the pouring process. Consequently, metal pouring operation using this refractory body and extending rod combination extends processing time, and thus increases production costs.
U.S. Pat. No. 4,799,650 to LaBate discloses a slag retainer consisting of a tapered, circular refractory closure having a tapered, hexahedron-shaped refractory extension. The circular closure is sized sufficiently to close the tap hole. A metal rod is passed through the center of the circular closure and extends downwardly into the elongated hexahedron shaped extension to join the circular closure and the hexahedron-shaped extension. The hexahedron extension prematurely throttles the flow of molten metal through the discharge nozzle. Consequently, a significant amount of usable molten metal remains in the receptacle after the pour is stopped, substantially decreasing the total molten metal released per pour, and thus increasing operation costs.
U.S. Pat. No. 4,494,734 to LaBate et al. discloses a slag retainer with a modified cone-shaped refractory body and a rod. The rod extends below the center of the body and is covered with refractory sleeves. The upper extension contains a swivel mechanism which is used to engage a mechanical device that positions the slag retaining device over the tap hole. The patent also covers a method of minimizing slag carryover by dropping a body having a plurality of generally irregular faces and a guide means within a restricted area, draining a furnace, monitoring the stream for flaring, and shutting off flow through the tap hole. Unfortunately, continuous intrusion of the guide means extends the time for discharging metal and may encourage operators to prematurely terminate the flow of the molten metal. Additionally, the process of constructing and affixing refractory sleeves to the downward extension significantly increases the cost of manufacturing the slag retainer.
U.S. Pat. No. 4,709,903 to LaBate discloses a slag retainer consisting of a barrel shaped refractory body and a rod. The rod extends vertically through the barrel shaped body and upwardly and downwardly thereof. The upward extension is engaged to a mechanical device used to position the slag retaining device over the tap hole. The downward extension is covered with refractory sleeves. However, the downward extension enters the tap hole and continues to prematurely restrain the flow of molten metal through the discharge nozzle. Consequently, as previously discussed, the problem of premature termination of the pour results. The problems of shaping and assembling previously discussed are also encountered.
U.S. Pat. No. 4,610,436 to LaBate, II et al. discloses a slag retaining closure having a tapered body and an elongated guide means consisting of an elongated guide member and tip portion depending from the closure. A tip portion of the guide member having a recess or a cavity accelerates and aligns the guide member with the tap hole. The portion of the guide member extending below the tapered end of the closure is coated with refractory sleeves. As with the other disclosures, operation costs are increased due to premature throttling and pour termination. Moreover, the use of the intricate elongated guide means substantially increases manufacturing complexity and has been disfavored.
The previously known refractory body and extending rod combinations suffer from additional disadvantages. These combinations require pre-assembly. The resulting unit requires special packaging to ensure that the extending rod does not break off during delivery. Additionally, the cumbersome shape of the body and rod combination decreases the amount of units that can be shipped in any given space. Moreover, the elongated rods of existing devices may strike the wall of the receptacle instead of entering their intended position in the tap hole. Since the vortex forms above the tap hole, incorrectly positioned devices have little or no effect on inhibiting the vortex. The shipping and operational problems contribute to a lack of industry acceptance of vortex inhibitors with a body and rod combination.
The present invention overcomes the abovementioned disadvantages by providing a vortex inhibitor using a refractory body with a hollow chamber adapted to receive a sacrificial member. The vortex inhibitor has a specific gravity less than the specific gravity of molten metal and is self-orienting in a narrow end downward position in a molten metal bath. The sacrificial member does not inhibit the flow of the molten metal since it can dissipate shortly after introduction into the metal bath. Additionally, even if the sacrificial rod strikes the wall of the receptacle, the rod can dissipate shortly after introduction into the receptacle, thus freeing the body to relocate to the area in which the vortex forms. Furthermore, the sacrificial member may be constructed of inexpensive metal rod, bar, pole, or other types of elongated members such as tubes, rather than the intricate and expensive guide systems of the prior art.
In general, the vortex inhibitor of the present invention comprises a tapering, castable refractory body, a hollow chamber positioned longitudinally to the axis of tapering of the body, and an elongated sacrificial member carried by the hollow chamber. It is to be understood that the term castable refractory is a uniform mixture, but uniform does not require complete homogeneity of material and includes the intermixture of shot, steel fiber or other materials which may be consistently mixed with a castable refractory material to adjust the specific gravity of the body. In any event, the specific gravity of the uniform mixture is selected so that the body and sacrificial member combination is buoyantly supported at the interface of the slag layer and the molten metal layer. Moreover, the vortex inhibitor of the present invention does not require assembly before shipping, thus reducing the difficulty and cost associated with shipping previously known bodies with guides.
The body has a generally tapering shape along a longitudinal axis from a base toward a narrow end. The term generally tapering means that the body generally conforms with the shape of the vortex formed by the swirling molten metal above the discharge nozzle. The cross-sectional area of the base is greater than that of the narrow end. As used herein, the term narrow end is to be understood as not defining any particular shape, and may include a pointed end, a rounded end or a flat surface. The base can be formed from a simple or complex polygon, or a rounded or circular figure. Complex polygonal bases may include flats, recesses or notches. These features may extend lengthwise along the body. The taper is preferably consistent along the length of the body. The refractory body is preferably constructed by creating a mold of the generally tapering shape.
The hollow chamber is positioned longitudinally to the longitudinal axis of the body and extends within the body. The mold used to construct the refractory body has an insert, preferably in the form of a shaft which forms the hollow chamber during the curing process. Depending on the application, the shaft may be separated from the refractory body or retained within the refractory body once the molded mixture cures. If the shaft is separated from the refractory body, the resulting empty hollow chamber snugly receives the elongated sacrificial member. If the shaft is retained after construction, the sacrificial member is attached to an end of the shaft. In either event, when introduced into the molten metal receptacle, the hollow chamber may fill with molten metal that forms a core within the refractory body. The metal core helps orient the refractory body in a narrow end downward position.
The sacrificial elongated member may be constructed of hollow or solid metal and can be coated with a refractory material. If the elongated member is hollow, then the hollow can be filled with refractory material, as well. When the vortex inhibitor is placed in a molten metal receptacle, the sacrificial member can align the vortex inhibitor with the area in which the vortex would be likely to form. As the pouring process continues, the sacrificial member can dissolve into the molten metal bath, and thereby does not interfere with the flow of molten metal through the discharge nozzle.
Thus, the present invention provides a vortex inhibitor having a refractory body, a hollow chamber within the refractory body and a sacrificial member. These features help orient the refractory body so that its narrow end extends downwardly toward the discharge nozzle of a molten metal receptacle while not reducing the flow of molten metal through the discharge nozzle. When inserted into a molten metal bath, the resulting body and sacrificial member combination has a specific gravity less than the specific gravity of the molten metal. Preferably, the refractory body maintains a center of gravity closer to the narrow end than a center of buoyant support even when the rod has dissolved. Additionally, since the elongated member is sacrificial, it can dissolve before creating a throttling effect upon the discharge flow.
As a result, the present invention permits substantially complete drainage of the furnace with minimal intermixture of the slag and molten metal layers. Moreover, it will be understood that the present invention can also be used for other molten metal receptacles, such as ladles and tundishes, in which separation of the slag from molten metal must be maintained while the metal is discharged from the receptacle.